Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein which transport all fat molecules around the body in the extracellular water. These groups, from least dense, compared to surrounding water (largest particles) to most dense (smallest particles), are chylomicrons (aka ULDL by the overall density naming convention), very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein and high-density lipoprotein (HDL). LDL delivers fat molecules to the cells and can drive the progression of atherosclerosis if they become oxidized within the walls of arteries.

    It is important to note that LDL is not "bad cholesterol". It is an essential transport system for lipids the human body needs to survive, including cholesterol. There is both "large" and "small" particle LDL, and while only small is associated with cholesterol-related issues, neither is "bad". Even "small" LDL is necessary to conduct nutrients to vessels that "large" LDL can't reach.